1. Field of the Invention
The present invention relates to an image pickup apparatus, a method of controlling the same, and a storage medium, and more particularly to an image pickup apparatus including analog-to-digital converters.
2. Description of the Related Art
In general, in a case where there is a high-luminance object, such as headlights or sunlight, within a shooting area, an image obtained as a result of shooting is required to have no so-called whiteout caused thereon, and what is more, have no blackout caused in a low-luminance area thereof. That is, to shoot an image under such a condition, a wide dynamic range image is required.
To obtain a wide dynamic range image, first, a low-sensitivity image suitable for a high-luminance object and a high-sensitivity image suitable for a low-luminance object are obtained. Then, image processing is performed on these images of the two types to thereby generate a wide dynamic range image. To this end, there is a demand for a solid-state image pickup apparatus, such as a CMOS image sensor, which is capable of simultaneously obtaining a low-sensitivity image and a high-sensitivity image.
In addition, although conventionally a progressive moving image having a frame rate of 30 Hz and an interlace moving image having a frame rate of 60 Hz have been generally used as moving images, with an increase in the operating speed of display devices, there is a demand for a solid-state image pickup apparatus which is capable of shooting a progressive moving image at a frame rate of 60 Hz or shooting an image at a higher frame rate than 60 Hz. If it is possible to perform imaging at a high frame rate, it becomes possible to accurately capture a motion of an object moving at a high speed. Further, by using such a solid-state image pickup apparatus capable of performing high-frame rate imaging, it is possible to synthesize a plurality of images and perform image processing to improve the S/N ratio and expand the dynamic range.
There has been proposed a solid-state image pickup apparatus including two or more analog-to-digital converters (ADCs) provided for each column of pixels and configured to perform high-frame rate imaging by distributing outputs from pixels in each column to these analog-to-digital converters to thereby achieve high-speed imaging by parallel processing (see Japanese Patent Laid-Open Publication No. 2005-347932).
Further, there has been proposed a solid-state image pickup apparatus having unit pixels each provided with a first photodiode and a second photodiode lower in optical sensitivity than the first photodiode, for photoelectrically converting and accumulating incident light, so as to increase the dynamic range. This image pickup apparatus has a high-sensitivity mode for outputting a signal generated by amplifying a potential obtained by reading out and adding signal charges from the first and second photodiodes, and a low-sensitivity mode for outputting a signal generated by amplifying a potential obtained by reading out the signal charge from the second photodiode (see Japanese Patent Laid-Open Publication No. 2011-15219). By switching these modes, the sensitivity is increased when the amount of incident light is small, and is reduced when the amount of incident light is large, to thereby prevent outputs from the unit pixels from being saturated and increase the dynamic range.
Further, there has been proposed a solid-state image pickup apparatus including a pixel section formed by arranging a plurality of pixels in a matrix form in which each pixel includes a plurality of divisional pixels formed by dividing the one pixel into areas which are different in the amount of charge to be accumulated, and when reading out a pixel signal, divisional pixel signals from respective divisional pixels are read out and added after being subjected to analog-to-digital conversion to thereby obtain pixel signals of respective pixels (see Japanese Patent Laid-Open Publication No. 2010-28423).
As described above, Japanese Patent Laid-Open Publication No. 2005-347932 discloses a method for performing high-frame rate imaging, and Japanese Patent Laid-Open Publication No. 2011-15219 and Japanese Patent Laid-Open Publication No. 2010-28423 each disclose a method for increasing the dynamic range. However, a method for increasing the dynamic range and performing high-frame rate imaging is not disclosed.
Particularly, when one pixel includes a plurality of photodiodes, as disclosed in Japanese Patent Laid-Open Publication No. 2011-15219 or Japanese Patent Laid-Open Publication No. 2010-28423, it is difficult to read out pixel signals at a high frame rate.